Bad cavities and masers

Often when I read papers about state-of-the-art lasers (in terms of linewidth and stability), many mention (e.g. here, figure 1: http://arxiv.org/pdf/physics/0512096.pdf) that the Hydrogen-maser works in the bad-cavity limit. I don't know why that is and I can't seem to find any good litterature explaining this.

Being in the bad-cavity limit means two things: First, the cavity lifetime is rather short, which means that the cavity quality factor is not too high. Second, the cavity lifetime is much shorter than the typical light-matter interaction timescale and also shorter than the decay timescale of your active medium. That means you are also far away from the strong coupling limit.

This should be explained in the Mandel/Wolf book on quantum optics, I think, but it is a hard read. Kavokin's book on microcavities also explains those things, but is obviously not focused on lasers in general. Maybe Haken's book also explains this.

Most of the good maser books were written >30 years ago and are out of print (I have access to some of them because I have a collegue who works with masers ands he has been collecting materials for years).
However, there are a few review articles out there that migth be helpful. Keep an eye out for articles on frequency references (the main application of hydrogen masers). Unfortunately I can't think of a good reference now, but I can have a look when I get into the office on Monday.